1. Field of the Invention
The present invention relates to a near-field light generator including a waveguide and a plasmon generator, and to a thermally-assisted magnetic recording head including the near-field light generator.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of a recording medium. The slider has a medium facing surface that faces the recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of a recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating the near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
JP-A-2011-86361 discloses a thermally-assisted magnetic recording head configured to excite plasmons on a plasmon generator (a light emitting part) by directly irradiating the plasmon generator with laser light.
U.S. Patent Application Publication No. 2010/0172220 A1 discloses a thermally-assisted magnetic recording head in which a plasmon generator (a surface plasmon antenna) is arranged to face the outer surface of a waveguide (a core) with a predetermined distance therebetween, so that light propagating through the waveguide is totally reflected at the outer surface of the waveguide to thereby generate evanescent light that is used to excite surface plasmons on the plasmon generator.
The configuration in which the plasmon generator is directly irradiated with laser light to excite plasmons on the plasmon generator, such as one disclosed in JP-A-2011-86361, has a number of problems as follows. First, this configuration has the problem of low efficiency of transformation of laser light into near-field light because most part of the laser light is reflected at the surface of the plasmon generator or transformed into thermal energy and absorbed by the plasmon generator. Further, this configuration has the problem that the plasmon generator greatly increases in temperature when it absorbs thermal energy, and this may result in corrosion of the plasmon generator. Further, this configuration has the problem that the plasmon generator expands as it increases in temperature, and may thus protrude from the medium facing surface to cause damage to a recording medium or to itself.
The configuration in which evanescent light is used to excite surface plasmons on a plasmon generator, such as one disclosed in U.S. Patent Application Publication No. 2010/0172220 A1, provides higher efficiency of transformation of laser light into near-field light when compared with the case of directly irradiating the plasmon generator with laser light. This makes it possible to resolve the above-described problems.
The thermally-assisted magnetic recording head disclosed in U.S. Patent Application Publication No. 2010/0172220 A1 has a problem that the ratio of a part of the outer surface of the plasmon generator, the part being opposed to the outer surface of the core, to the entire outer surface of the plasmon generator is small, and it is thus difficult with this head to excite a lot of surface plasmons on the plasmon generator.